Regulation of gene expression is controlled at the level of RNA transcription. We propose in this application to investigate the regulation of expression of a set of inducible genes of Drosophila melanogaster termed the "heat shock genes." When Drosphila are shifted from the normal growth temperature of 25 degrees centigrade to 37 degrees centigrade, the synthesis of at least 7 proteins is induced. Since the response to heat shock begins quickly after the temperature shift, the system can be treated as a "classical" inducible system. Furthermore, most genes actively transcribed prior to heat shock are subsequently repressed. Recombinant DNA technology has been exploited to isolate the heat shock genes. The primary DNA sequence of the regions surrounding the 5' end of the mRNA coding regions has been determined and compared. Some homotology has been found near the point of initiation of transcription and 195 bases upstream from that point. Heat shock genes from other species will be compared to see if these regions are also conserved during evolution. Also we propose to set up an in vitro transcription system which will allow us to test "mutants" constructed in vitro which contain alterations in putative regulatory regions.